Find out who's at the door by answering your phone. When a visitor presses the doorbell on the Brass Telephone Entry System Intercom, it sends a distinctive ring to every telephone in your house. This intercom integrates a weather-resistant speaker/microphone with a doorbell button, which triggers the Telephone Entry Controller (sold separately) to signal you through your phone lines. This system adds safety and convenience to answering the door by allowing you to speak to visitors from any phone in the house before opening your door.